Justified returns (FX, 10 p.m. ET) tonight, and unlike in year’s past, when the season-long arc was Marshal Raylan Givens (Timothy Olyphant) chasing one formidable bad guy, season 4 revolves around one formidable mystery. As the premiere opens, we flash back 30 years ago, to a man falling from the sky with a parachute and a bag of cocaine. The story behind that is something Raylan’s incarcerated father, Arlo (Raymond J. Barry), could help unravel. ”Arlo’s confronted with that and does something in the first episode that we hope is shocking,” exec producer Graham Yost says, ”and that’s part of what sets the whole mystery in motion.”

What else can you expect from season 4? Here, Yost offers more teases.

• The season is divided into three parts. Raylan and Boyd (Walton Goggins) will be too busy with their own arcs to see each other until the fifth episode. In the premiere, Raylan begins moonlighting as a bounty hunter. “He’s trying to bank a little cash in anticipation of his child being born. He’s sort of afraid that Winona might not grant him visitation if he’s living above a bar, so maybe he should grow up a little bit and get a real place,” Yost says. “But of course, the only way he can think of to make extra money is to do things that are not allowed by the Marshals service, like tracking down an out-of-state bail jumper. One of the interesting things about Kentucky is there are no bounty hunters allowed. So, into that vacuum Raylan steps in the first episode to get a guy – and without giving it away, there will be a ripple effect from that later on in the season.” That story line also intersects with the introduction of Patton Oswalt’s recurring character, Constable Bob Sweeney, who Raylan has hired to watch Arlo’s house. Oswalt filled us in on him here.

Boyd, meanwhile, will see his Oxy revenue threatened by the arrival of Preacher Billy (Joe Mazzello) and his sister Cassie (Lindsay Pulsipher), who are saving Harlan’s sinners. “Billy and Cassie have come from a family of Holiness churches. It involves snake-handling. The real term for people like that is signs followers, and it comes from scripture – it’s basically that you can handle serpents and the Lord will protect you, you can drink poison and the lord will protect you, the Lord will protect you from devils. And of course, into Billy’s life comes Boyd, because Boyd sees this church as a challenge to him,” Yost says. “In the first episode, you’ll see that he’s trying to get money out of a dealer who’s been selling Oxy for him, and the dealer has not been selling, and he says he’s been saved by this church. And then we’ll also find in that first episode, that dear Ellen May [Abby Miller], one of the whores at the brothel that Ava [Joelle Carter] runs, has been pulled into the church as well. And one of the fears from that for Boyd and Ava is, is she gonna try to unburden her soul and say that she and Ava killed [Ava’s pimp] Delroy last season? So that becomes part of the risk.”

Once Raylan and Boyd’s stories cross in the fifth episode? “Then they are at cross-purposes for the rest of the season,” Yost says. “Our goal is to really heat that up by the end.”

• Raylan is still with bartender Lindsey (Jenn Lyon). Yost doesn’t want to spoil it, but starting in episode 2, she brings a new complication into Raylan’s life. As for Raylan’s pregnant ex Winona (Natalie Zea, now starring on Fox’s The Following), the first time we’ll see her is in episode 5.

• The rest of the Marshals office gets their due: “We look for a big story for each of them, in terms of where are they this season,” Yost says. For Art (Nick Searcy), it comes in episode 2. “We’re gonna find out something else about Art. It’s not soapy – he doesn’t have some dreaded disease – it’s just something that’s the natural course of being a Marshal,” he says. For Rachel (Erica Tazel), it’s episode 3. “We’re gonna find out that unbeknownst to us, she was married and that’s not lookin’ good right now. And how does that reflect back on Raylan and his relationship troubles? So they go on a bit of an adventure together.” And as for Tim (Jacob Pitts), “We’ve found it’s just so much to have him on any case with Raylan – he just gives Raylan such a hard time, and it’s so wonderful – so he’ll continue to play that function,” Yost says, starting with a stakeout in episode 2. “But then in our sixth or seventh episode, we’re gonna start a story that just involves him and play that out over a few episodes.” Yost is cagey about that: “It starts personal, then crosses over into professional.”

• Wynn Duffy (Jere Burns) sees more screentime. “There’s always talk in the [writers] room, ‘Should Raylan kill Wynn Duffy?’ And it’s like, ‘No, we just love him so much.’ We love Jere. We love that character, so Wynn Duffy plays a big part in this season,” Yost says. He’ll start off at odds with Boyd. “There’s a lot of conflict,” Yost says, “but in the fifth episode, you see that they have to work together.” (That’ll be fun. “Yes,” Yost confirms.) Look for that arc to involve Johnny (David Meunier). “Johnny betrayed Boyd [last season] and you will see that continue,” Yost says. “So there’s actually not a lot of questions, it’s just how is that gonna play out?”

• Episode 4 is critical for Ava and Boyd. “With Ava, there’s a little bit of this sense of what are we doing this for? Something pivotal happens in the fourth episode, where Ava and Boyd make a choice that seems to sort of damn their souls, in a way, but they get past that with sort of a renewed vigor for their plans for the future,” Yost says. “For a lot of characters, [the season is about] the things you do for the future, for your offspring, for the next generations, the choices you make. It all seems worth it. There’s that feeling that the ends justify the means. But sometimes, the means are pretty awful. Or, in the case of Raylan, just against the law. That’s a theme that plays out.”

• Bonus scoop! When producer/writer Chris Provenzano and executive story editor Ingrid Escajeda took a research trip to Harlan for season 4, they had certain requests from the writers room, Yost says: “Look into snake-handling churches, look into stories we heard of swinger parties up in the hills.”

So are we going to see the latter? “Well, I will not say when. But there will be something.”

Come back to Inside TV tonight for the first of our weekly season 4 postmortems with Yost. We’ll also be recapping the show this season.